The precise estimation of small quantities of injected fuel is necessary in order to adjust the injection parameters of the injection system precisely to the area of small injection quantities. This forms the basis for the ability to inject a requested quantity of fuel consistently and reliably so that the new European emission standards for new vehicles can be observed. In this context it should be noted that undesired emissions from internal combustion engines are particularly sensitive to imprecise setting of injection parameters in the area of small injection quantities.
Most motor vehicles have a crankshaft sensor which records the angular velocity of the crankshaft. This variable provides an excellent source for deducing dynamic values derivable from individual combustion events in the cylinder. Previous technical arrangements have employed high-resolution noise measurement in the engine with the aid of one or more microphones or knock sensors. These are attached to the engine unit near the cylinder. According to a further alternative, cylinder pressure measurements are taken with the aid of a cylinder pressure sensor. Cylinder pressure sensors may be arranged in various positions inside the cylinder. However, both approaches have the disadvantage that they are not installed in motor vehicles as standard and therefore increase the manufacturing costs of the vehicle substantially.
Known approaches from the prior art for estimating injection control parameters include the estimating of an isolated point according to an actuation time of an electrical injection system in which combustion can be recorded (cf. DE 198 09 173 AI and DE 199 45 618 A1). Another method tries to estimate the torque resulting from an isolated injection. This approach can also be used to assign the injection parameters to the injected fuel quantities in an open control loop. This approach also involves the assignment being based or estimated on several different points in order to thus provide greater precision. However, the method has the disadvantage that the information from the estimated points is not used jointly.
Other approaches in turn describe the adjustment of energy supplied to a piezo-injection system instead of the adjustment of an actuation time to the injection system in order to thus identify and correct the assignment of the injection parameters to individual injection quantities. All these approaches are based on injected fuel quantities or torques being determined from isolated injections by estimating the speed signals of the crankshaft or the signals of the crankshaft sensor in the internal combustion engine.